Oscillators can be used in integrated circuits for various purposes. For example, a voltage controlled oscillator can be associated with a phase-locked loop (PLL) module to generate an internal clock signal having its phase locked to a received signal. The PLL module may include a phase detector coupled to the voltage controlled oscillator. The phase detector may detect a phase difference of the internal clock signal and the received signal. The phase difference can be converted to a voltage signal. The voltage signal can be used to vary an oscillation frequency of the voltage controlled oscillator, such that the phase of the internal clock signal can be locked to the received signal.